HIV-1 causes neurocognitive and neurological disorders that represent a public health problem as they result in a substantial burden to patients living with HIV infection, their caregivers, and the healthcare system. A recent report suggests that clade C viruses may possess a reduced capacity for neuroinvasion because clade C isolates bear tat sequences coding for a variant Tat protein shown in vitro to be defective in monocyte chemotaxis as compared to clade B Tat. The defective Tat chemokine motif is hypothesized to be clade C-specific based on isolates from several countries and could explain the lower prevalence of HIV brain involvement reported in some of these countries. However, no study has directly compared neurocognitive function among individuals infected with HIV-1 clades C and B. Thus, lower reported rates of dementia in regions where clade C is prevalent may result from ascertainment bias, differential prevalence of co-infections or other factors. This application proposes to perform a cross-sectional comparison of the influence of HIV-1 clade on neurocognitive and neurological disorders in southern Brazil. UCSD investigators, who have extensive experience in NeuroAIDS clinical research, will support investigators in Curitiba, Parana, Brazil, who care for large numbers of patients infected with either clade C or B. In this setting, clade-specific effects can be compared while controlling for potential confounding factors such as ethnicity, sociodemographic characteristics, risk factors for HIV infection and co-infections. UCSD investigators will train and guide the administration and interpretation of the clinical assessment instruments, transfer technology to the Brazilian site. [unreadable] [unreadable]